fairing

[cat man do]

Originally Posted by northerncat

also how long does glass stay green for generally?, i have been using 6-8 hr intervals but how long can you leave it for?
sean

Wow , that could be scary in the tropical heat.

Usualy if you can push your thumbnail into the glass it is still green , if it is still just tacky it is still green, if it is hard enough to scratch with sandpaper it has gone off. Even if it clog's the paper you should wait until it's kicked further , sand , wipe with metho and go again.

Dave

[northerncat]

dont say that that makes me scared!!! i had been told that it would still have a chemical bond with previous epoxy provided that it was under 24 hours old, i just asked because i have started to wonder about this seeing as im on my second lot of fairing now and have started to put a little more thought into it than i did when i glassed and faired the hulls
sean

[cat man do]

Information from the West System siteWEST SYSTEM Epoxy Epoxy chemistry

Epoxy's cure stages

Mixing epoxy resin and hardener begins a chemical reaction that transforms the combined liquid ingredients to a solid. The time it takes for this transformation is the cure time. As it cures, the epoxy passes from the liquid state, through a gel state, before it reaches a solid state (Figure 1). As it cures, mixed epxoy pass from a liquid state, through a gel state, to a solid state.

1. Liquid-Open time Open time (also working time or wet lay-up time) is the portion of the cure time, after mixing, that the resin/hardener mixture remains a liquid and is workable and suitable for application. All assembly and clamping should take place during the open time to assure a dependable bond.
2. Gel-Initial cure The mixture passes into an initial cure phase (also called the green stage) when it begins to gel or "kick-off." The epoxy is no longer workable and will no longer feel tacky. During this do not disturb stage it progresses from a soft gel consistency to the firmness of hard rubber. You will be able to dent it with your thumbnail.
Because the mixture is only partially cured, a new application of epoxy will still chemically link with it, so the surface may still be bonded to or recoated without special preparation. However, this ability diminishes as the mixture approaches final cure.
3. Solid-Final cure The epoxy mixture has cured to a solid state and can be dry sanded and shaped. You should not be able to dent it with your thumbnail. At this point the epoxy has reached about 90% of its ultimate strength, so clamps can be removed. It will continue to cure over the next several days at room temperature.
A new application of epoxy will no longer chemically link to it, so the surface of the epoxy must be properly prepared and sanded before recoating to achieve a good mechanical, secondary bond. See Surface Preparation
Understanding cure time
Open time and cure time govern much of the activity of building and repairing with epoxy. Open time dictates the time available for mixing, application, smoothing, shaping, assembly and clamping. Cure time dictates how long you must wait before removing clamps, or before you can sand or go on to the next step in the project. Two factors determine an epoxy mixture's open time and overall cure time-hardener cure speed and epoxy temperature.
Hardener speed
Each hardener has an ideal temperature cure range. At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. The product guide and container labels describe hardener pot lives and cure times.
Pot life is a term used to compare the cure speeds of different hardeners. It is the amount of time a specific mass of mixed resin and hardener remains a liquid at a specific temperature. (A 100g-mass mixture in a standard container, at 72°F). Because pot life is a measure of the cure speed of a specific contained mass (volume) of epoxy rather than a thin film, a hardener's pot life is much shorter than its open time.
Epoxy temperature
The warmer the temperature of curing epoxy, the faster it cures (Figure 1). The temperature of curing epoxy is determined by the ambient temperature plus the exothermic heat generated by its cure.
Ambient temperature is the temperature of the air or material in contact with the epoxy. Air temperature is most often the ambient temperature unless the epoxy is applied to a surface with a different temperature. Generally, epoxy cures faster when the air temperature is warmer.
Exothermic heat is produced by the chemical reaction that cures epoxy. The amount of heat produced depends on the thickness or exposed surface area of mixed epoxy. In a thicker mass, more heat is retained, causing a faster reaction and more heat. The mixing container's shape and the mixed quantity have a great affect on this exothermic reaction. A contained mass of curing epoxy (8 fl. oz. or more) in a plastic mixing cup can quickly generate enough heat to melt the cup and burn your skin. However, if the same quantity is spread into a thin layer, exothermic heat is dissipated, and the epoxy's cure time is determined by the ambient temperature. The thinner the layer of curing epoxy, the less it is affected by exothermic heat, and the slower it cures.
Controlling cure time
In warm conditions use a slower hardener, if possible. Mix smaller batches that can be used up quickly, or pour the epoxy mixture into a container with greater surface area (a roller pan, for example), thereby allowing exothermic heat to dissipate and extending open time. The sooner the mixture is transferred or applied (after thorough mixing), the more of the mixture's useful open time will be available for coating, lay-up or assembly.
In cool conditions use a faster hardener, or use supplemental heat to raise the epoxy temperature above the hardener's minimum recommended application temperature. Use a hot air gun, heat lamp or other heat source to warm the resin and hardener before mixing or after the epoxy is applied. At room temperature, supplemental heat is useful when a quicker cure is desired.
For detailed information on working with epoxy at low temperatures, refer to 002-915 Cold Temperature Bonding and Coating with Epoxy.
CAUTION! Heating epoxy that has not gelled will lower its viscosity, allowing the epoxy to run or sag more easily on vertical surfaces. In addition, heating epoxy applied to a porous substrate (softwood or low-density core material) may cause the substrate to "out-gas" and form bubbles in the epoxy coating. To avoid out-gassing, wait until the epoxy coating has gelled before warming it. Never heat mixed epoxy in a liquid state over 120°F (49°C).
Regardless of what steps are taken to control the cure time, thorough planning of the application and assembly will allow you to make maximum use of epoxy's open time and cure time.

I realize that you may not be using West Sysytem Epoxy, neither am I, but the same rules apply to all epoxy.

Hope this helps Sean

Also look at epoxy works which you can access from thay site

Dave

[Stevens 47]

Northerncat

You may want to try a technique called ribboning. You basically use a serrated blade (similar to flooring glue) to apply the the fill, it will leave grooves you fair the grooves to shape then fill after. Saves alot of material and time. I saw the technique in a article out of the Professional Boat builder mag (online as well). The article was covering a AC boat in Auckland that had broken in half. They cut the hull clean through added 9 feet then faired it. Had the thing back in the water in about 45 days from the day it broke.

Jack

[knottybuoyz]

Short photo essay on the fairing of a hull section for a Farrier 39.

Fairing and painting the second float

Interesting process but wouldn't it use a lot of material and increase the weight of the hulls?

[cat man do]

Originally Posted by Stevens 47

Northerncat

You may want to try a technique called ribboning.
Jack

Have had a go at this and unless you can be guaranteed of having the same density bog as the beads, you can end up seeing ridges in the final job.

Also for the fussy amongst us I was worried about not having a chemical bond on the sides of the ridges.

Dave

[northerncat]

hmm ill have to rethink my strategies i think, i have high pressure hosed both of the hulls off and no fairing came off so this is a good sign, i think ill glass the whole hull and decks and then just scuff tt all back before doing a big hit with the fairing compound, thanks for the info guys, i tried the trowel method but hated the full on application of fairing twice, i can trowel it on pretty well having had a bit of experience in this area i think ill try the mayonaise consistency as i probably have been mixing it a bit to dry i have been trying to aim for compound with a wet look and when you hold it on the mixing spatula itll just slowly fall off
sean

[cat man do]

Sean, as I did most of the glassing without help, I did a drop of glass which would take about 1.5 hours, then do the next one , the overlap get's a good chemical bond still.

Go back and bog the first one and by then the second has probably kicked and you can bog this as well, leaving 100mm in from edge so as to start drop 3.

If running out of time, bog out and past edge 50mm, and the next day, just run the 2 speed down the edge sanding back to glass, without actually sanding glass, and leaving a nice feathered edge.

Easy

With the bog, I actually have it so It will slowly pour from the container, thick tomato sauce, runny mayo.

If you only have a cuppla mm of bog it won't sag, but gee it's easy to spread.

Being a strip plank hull I spent a fair amount of time setting up my frames and then planeing/sanding hull so it was fair before I glassed. I'd rather work with the timber than bog.

Needless to say, it's really just the glass overlaps we had to worry about.

I reckon the highbuild is almost thicker than the bog on most of the boat.



Dave

[northerncat]

do you reckon you could roller the high build with the qcell or is it to thick, i dont have access to a you beaut spray gun like you so roller would be the cheaper option, otherwise ill have to go out and buy a bigger nozzle spray gun, which is !!sigh!! more money!!
sean

[Whimsical]

Sean I think Dave should just come and do yours, when he's finished he can head on over here and do mine.
Well he did say he enjoyed fairing.
Mike

[cat man do]

Originally Posted by Whimsical

Sean I think Dave should just come and do yours, when he's finished he can head on over here and do mine.
Well he did say he enjoyed fairing.
Mike

Nah mate, I think youll find it was a mate that likes fairing, I'd rather slash my wrist's.

I'm pretty handy, just hate the job.

Dave

[cat man do]

do you reckon you could roller the high build with the qcell or is it to thick, i dont have access to a you beaut spray gun like you so roller would be the cheaper option, otherwise ill have to go out and buy a bigger nozzle spray gun, which is !!sigh!! more money!!
sean

Have a bit of an ask around Sean, some of the builders and suppliers will have done this, and we did the last cat with a compressor and 1 litre pot so it can be done, just not as fast.

Hire places usually have a big airless, just don't tell them you are spraying epoxy. It may cost a couple of hundred to rent, but you'd have yor boat blown in a day.

I really don't think you'll have a result with a roller, but do a section, and tip it of with a brush and see if it work's, sound's like a prick of a job though.

Dave.

[Stevens 47]

Have had a go at this and unless you can be guaranteed of having the same density bog as the beads, you can end up seeing ridges in the final job.

Also for the fussy amongst us I was worried about not having a chemical bond on the sides of the ridges

I meant noodling not ribboning. I will take some pics of a mates shock 35 and post them he is using this technique. The shocks and alot of flat spots.

In regards to rolling on fairing my other mate next to the shock is not as good with a trowel he rolled on micro balloons worked OK not great, more air bubbles that I would care for.

In regards to using a roller. I came across this idea for creating a non skid deck, I am going to experiment with it. Had a look at a new Santa Cruz 53 looks like they had done something similar to it to finish the under side of there hard dodger.

Jack

Seal the deck with 2-3 coats of epoxy as usual. Mask off areas to be non skid.
Mix epoxy with silica filler as you would for really thick glue. Apply to the masked areas and roll it out with a mohair roller. Result looks very professional.
Wash off any alamine when dry then apply several coats of paint. You may need to give it light sand before painting to knock off any real sharp bits

[Stevens 47]

Pics of Boat with Noodling.

The first pic show a striped area that was the very outside edger of the original noodle.


The second pic. Micro balloons and epoxy was first applied with a serrated trowel over the entire bottom, this was then faired then the groves where filled in more fairing. The groves sand faster and use less material.

Jack

[colemj]

Originally Posted by Stevens 47

Seal the deck with 2-3 coats of epoxy as usual. Mask off areas to be non skid.
Mix epoxy with silica filler as you would for really thick glue. Apply to the masked areas and roll it out with a mohair roller. Result looks very professional.
Wash off any alamine when dry then apply several coats of paint. You may need to give it light sand before painting to knock off any real sharp bits

I did this on my previous boat, only with gelcoat instead of epoxy. Exceeded my expectations - nice pattern, very good grip, yet not too harsh on bare skin. The use of colored gelcoat meant that I didn't need to paint. Gelcoat has held up well over the years, but it could be easily sanded off and reapplied in the future if needed. This might be more difficult with epoxy.

Mark